When we say “pass out,” we mean faint or become unconscious. The medical term for this is “syncope”, a word from Greek that basically mean to “cut off.” There are a multitude of reasons as to why someone might pass out, and we are sure you’ve all watched movies where someone passes out after hearing bad news (in older films it was always women), or perhaps when someone doesn’t have what it takes to watch an autopsy being performed.

These situations could indeed make someone pass out, but so could low blood sugar, hypotension, a seizure, and if you’ve ever see the show The Sopranos, you’ll know that a bad panic attack can leave you on the floor, as well. Today we are going to look into this biological phenomenon, in this episode of the Infographics Show, What Happens When You Pass Out?

The main reason we pass out is because the brain suddenly receives less blood. A more detailed explanation is this. The brain has different parts to it, such as the cerebellum, the cerebrum, and the brain stem. It’s also split into the left and right hemispheres. For you to remain conscious, you must be getting constant blood flow to the brain, which gives oxygen and glucose to the brain’s cells. For you to be awake, we are told that something called the “reticular activating system” in the brain stem has to be turned on, and either the right or left side of the brain needs to be getting enough blood.

If the reticular activating system doesn’t the get blood it requires, it will turn off. If that happens, on the floor you go. The same will happen if both sides of the brain don’t get enough blood supply, oxygen or glucose, aka sugar. You can apparently have ok blood sugar but still faint if you are not getting enough blood to both sides of the brain or the reticular activating system. If you are still wondering what that is, the dictionary definition is as follows: “A diffuse network of nerve pathways in the brainstem connecting the spinal cord, cerebrum, and cerebellum, and mediating the overall level of consciousness.”

So those prone to fainting might have a medical condition such as low blood sugar, heart problems, anemia, or just low blood pressure. But that’s not always the case, and many healthy people with no existing medical conditions can pass out. By the way, head trauma is not seen as passing out. When this happens, we call it a concussion, and that’s an altogether different thing.

In fact, it’s said that passing out accounts for 3 percent of visits to the ER, and 6 percent of all visits to the hospital. What’s more common, and you’ve all probably had this at some point in your life, is getting lightheaded. This is called presyncope. The most common type of fainting is called a vasovagal attack, and this usually starts with some lightheadedness, maybe some nausea, a spinning room, and then your world starts to fade to black quite quickly.

The fainting episode, though, usually only lasts a few seconds. If it is prolonged, then it could be serious, so if you are with someone who is down for a while, call an ambulance. You might also twitch, but this doesn’t always mean you are having a seizure. When you are out, you are out, meaning you remember nothing, and when you come back, you are usually confused for a few seconds. In cases that are not obvious, you should get yourself a physical examination after fainting.

Some people faint just because they stand up too quickly. There’s a reason for this. Your blood vessels are always changing their width to make sure you have constant blood pressure. They might tighten or expand. If you have low blood pressure, you might not get enough blood to the brain and that’s why you can feel dizzy when you get up fast. You may even faint when you get up too quickly, which in the medical world is called postural hypotension.

You are probably wondering why someone might pass out when they hear the bad news that their dog got chewed up by a super-powerful lawnmower and are then shown the damage. This is the same reason why people might faint just by seeing a hypodermic needle or their broken bone sticking through their shin. It’s usually related to a life-threatening situation, which might just be the sight of a dead body or blood. These images can cause us great distress.

This shock will cause the blood pressure to rise rapidly and then drop suddenly. It’s the same when we faint from pain. This is also due to a spike in blood pressure followed by a drop. The chemical adrenaline makes the blood pressure go up and the chemical acetylcholine makes it go down, a kind of chemically induced biological rollercoaster ride. Something called the vagus nerve is stimulated and this causes the release of acetylcholine, slowing down the heart and preventing you from getting enough blood to your head. This nerve is stimulated due to things we’ve already talked about, such as seeing a body being examined by a pathologist, but also when we feel extreme pain.

Don’t feel bad if you are the person who is prone to this kind of fainting. It doesn’t mean that you are weak, it just means you are predisposed to fainting and that is often inherited. You might find that your usually healthy mom or dad also faints a lot.

But what might seem like someone fainting due to this rollercoaster of chemicals can also sometimes be psychological. So, someone could be told some bad news and pass out just because of the rush of emotions. It’s uncommon, but when it happens it’s called psychogenic pseudosyncope. This is known as a conversion disorder, meaning stress can cause physical problems. Freud talked a lot about this, stating that some people due to stress might for a while lose the use of a limb. You can also faint.

Another way healthy people might faint, believe it or not, is just because they are hungry. Yes, you might pass out ‘cos you’ve skipped a few meals. The reason, a drop in blood sugar, and we’ve already explained that the brain needs that sugar. So why faint when we are severely dehydrated, there’s no glucose in water? The reason is because the fluid in your blood decreases and this makes it difficult for your nervous system to keep your blood pressure at a normal rate. If it goes too low, bang, you’re out.

This all sounds kinda scary, but most of the time it’s nothing to worry about. As we say, you should probably go get a physical though if there’s no obvious causes, such as you holding your breath (preventing oxygen getting to the brain), or you’ve just witnessed someone’s head rolling down the street.

Will it happen to you? The U.S. National Institute of Health tells us out of the general population, 18.1–39.7 per 1,000 experience passing out. The rate is similar in men as it is for women, but as you get older, there’s much more chance of fainting, especially when you get past 70 years of age. “The annual mortality can reach between 18 and 33% if cardiac cause, and between 0 and 12% if the non-cardiac cause,” said the institute, so as we say, see a doctor after inexplicable fainting.

So, have you ever fainted? What was the reason? We’d love to know the story. Share it with us in the comments! Also, be sure to check out our other video called What is Stone Man Syndrome?! Thanks for watching, and, as always, don’t forget to like, share, and subscribe. See you next time!

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